1. Field of the Invention
The present invention relates to a friction material composition to be molded into a frictional material. Particularly it relate to a friction material composition in which not only the heat-forming time required for molding the composition into a friction material is short but also the performance of the friction material obtained is sufficiently satisfactory.
2. Description of the Related Art
A friction material containing asbestos as a base is conventionally used as a friction material applied to disc brake pads (which may be hereinafter called merely "pads"), brake linings, etc. for vehicles such as cars, railraod vehicles, etc. The bad influence of asbestos on health, however, has become an issue for about ten years. From this point of view, a non-asbestos friction material, or the like, has been developed as a friction material using no asbestos. The non-asbestos friction material takes the main current in the world and is diversified in kind.
Generally, the aforementioned friction material is produced by molding of a composite material (hereinafter referred to as "friction material composition") comprising: an asbestos base or inorganic fiber, organic fiber, metal fiber or a combination thereof used as a base; a friction modifier, an inorganic or organic filler, etc. added to the base as occasion demands; and a thermosetting resin, etc. added thereto as a binder for binding all materials as a whole. In the friction material composition for producing the friction material, a novolak type phenolic resin is generally used as the thermosetting resin used as a binder from the viewpoint of overall characteristics such as moldability, economy, heat resistance, etc.
Incidentally, the heat-forming time in the production of the friction material depends on the hardening reaction speed of the thermosetting resin used as a binder. In any one of known friction material compositions each using a novolak type phenolic resin as the thermosetting resin, however, there is a problem that expected good quality is hardly secured because the hardening state of the friction material obtained is apt to be insufficient if the hardening reaction time, that is, the heat-forming time is not sufficiently long. Therefore, a friction material composition using a novolak type phenolic resin, in which not only the performance of the resulting friction material obtained by use of the composition is sufficiently satisfactory but also the time required for hardening the binder, that is, the heat-forming time is short, needs to be developed for the purpose of reducing the cost in production of the friction material.